Rubio was a key player on the bipartisan "Gang of Eight" that conceived, wrote and pushed a Senate bill aimed at tightening border security, revamping the nation's visa program and providing a path to citizenship for an estimated 11 million undocumented immigrants.

The bill was approved 68-32 in June, a remarkably decisive outcome in a divided Senate. It has stalled in the House, where GOP leaders oppose the citizenship provision. They would rather address immigration through a series of smaller bills, most dealing with security.

Immigration activists praised Rubio for his courage following the Senate vote. Tea party activists denounced him for backing what they call "amnesty" for immigrants in the country illegally and said they were rethinking their support for him if he runs for president in 2016.

Now, Rubio's immigration strategy has abruptly pivoted from a comprehensive approach to the go-slow strategy backed by the House.

In interviews with reporters this week, the son of Cuban-American immigrants said he still supports a comprehensive bill but is being "realistic" about what can be achieved given the House's resistance. His spokesman, Alex Conant, confirmed the new tactic.

"Sen. Rubio worked very hard on immigration reform and we successfully passed it in the Senate, but now we're dealing with the political reality of what's achievable in the House," he said.

Rubio "is just trying to make progress on immigration reform, and the best way to make progress is to focus on what we agree on," Conant continued. "We should not waste another opportunity to begin to improve our immigration system, which is what will happen if people stick to an all-or-nothing approach."

That's not sitting well with immigration activists.

They view the move as a betrayal and an attempt by Rubio to revive his flagging presidential aspirations. Rubio's star has been somewhat eclipsed by Republican Sen. Ted Cruz of Texas, a fellow Latino tea party favorite for the White House who staunchly opposed the Senate's immigration bill.

"I've been working on this for 25 years and there's no question that the only way you fix any one part is to have a comprehensive approach that addresses all the parts," said Frank Sharry, executive director of the pro-immigration group America's Voice.

Rubio is "tacking to the right to make himself more electable in places like New Hampshire and Iowa," Sharry said. "This is about personal ambition, not a concern for proper policy."

Tea party activists aren't impressed either.

Kathy Jones, who chairs the Lee County Patriots in Florida, said she thinks Rubio might be trying to appease the Republican base. She said it won't work.

"There are so many of us who will never cast a vote for him again," Jones said. "Those of us who voted for him voted for him based on what he said he was going to do and what his beliefs were. And he stated too many times — unequivocally — (that he) will never support amnesty for illegals."

The Senate bill Rubio championed to conservative audiences would spend more than $40 billion to build more fencing along the Southern border and add more than 20,000 border agents. It would revamp the nation's visa program and beef up workplace verification to make sure jobs are held by legal residents. It also would offer immigrants in the country illegally a 13-year citizenship process, provided certain security benchmarks are met.

Under the House approach, the only bills likely to win approval are those related to security, or pro-business measures that would expand the agricultural workforce or increase the number of high-tech visas, Sharry said.

"Many Republicans want to pass pieces of immigration reform but not deal with the 11 million undocumented immigrants in America," he said. "How can you solve the problem of immigration without dealing with a population the size of Ohio?"

Sharry calls Rubio's latest move "flip-flopping."

But "flip-flopping isn't so bad if you're going in the right direction," said Bob Vander Plaats, who heads The Family Leader, a socially conservative organization based in Iowa, where the nation's first presidential caucus takes place.

Vander Plaats said conservative voters in Iowa don't like the Senate immigration bill but will give Rubio a full hearing if he decides to run for president.

"If he's still saying at the end of the day the plan we put forward is where I want to go, well, this isn't going to help him a lot then," he said. "If he's saying, 'I've got a change of heart, we need to secure the border, we need to make sure all these things are done before we start looking into the other process' — that would probably help him."

Susan MacManus, a political science professor at the University of South Florida, said Rubio seems to be practicing pragmatism.

"There's nobody that better represents the difficulties of immigration reform than Marco Rubio," she said. " No matter which way you zig or zag, you're going to run into roadblocks. It all comes down to whether reformers or tea party people can be moved themselves, or are they intransigent. And he's banked on the fact that something is better than nothing."